This invention relates to a gravure printing system including a printing unit which effectively carries out a washing operation and a plate cylinder exchanging operation, a washing unit which supplies and recovers washing solvent, and a reproduction system for effectively utilizing the washing solvent. The invention also relates to a method of washing the printing unit.
A gravure printing system generally comprises a paper supply unit, at least one, printing units, a printed paper discharge units, and a washing unit for washing the printing units.
In gravure printing, and particularly, in a case where a film such as a then cellophane is used as a material to be printed, it is required to wash an ink pan and an inking device including an ink circulation unit and also to wash out ink adhering to an outer surface of a plate cylinder in the printing unit at a time when an ink is changed to another color ink regardless of a multicolor or monocolor printing operation.
Recently, it is required for gravure printing technique to print many kinds of materials with a reduced number of lots. This requires much time and labour for frequently exchanging the plate cylinders and washing the inking device and the plate cylinder.
In the conventional technique, the plate cylinder is exchanged by manually holding the plate cylinder or using a conveying bogie provided with a vertically movable support table. The plate cylinder is washed immediately after the printing operation by rotating the plate cylinder at a low speed, pouring a liquid detergent from the upper portion of the rotating cylinder to wash the same, and then wiping off the wet surface of the washed plate cylinder with rags, for example, manually. Regarding the washing technique, the ink pan and associated duct means are first removed from the printing unit and the removed members are conveyed to a washing portion, usually apart from the working portion, at which the removed members are manually washed or washed by using a washing device.
Several problems occur in the printing system of the type described above, and particularly, in the washing operation of the plate cylinder and the inking device and the plate cylinder exchanging operation, as pointed out hereunder.
a. The washing of the plate cylinder of each printing unit requires heavy labour and much time for the workers.
b. The manual plate cylinder exchanging operation using the conveying bogie provided with a vertically movable support requires heavy labour and much time for the workers and also requires disassembly of the inking device which is generally located below the plate cylinder in the printing unit.
c. The removing and conveying works of the ink pan and the associated ducts or pipes to the washing portion requires heavy labour and much time for the workers.
d. The ink adhering to the respective members may often dry as they are conveyed to the washing portion and the washing out of the dried ink further requires much time and labour for the workers and also requires much detergent or another ink removing means, which is not economical.
e. The liquid detergent as a washing agent or solvent to be used is usually a volatile substance the vapour of which is generally harmful to the workers.
In addition, in a conventional technique, and particularly, where the plate cylinder is manually washed, the washing solvent and the used solvent are conveyed to and from the respective printing units by means of conveying bogie or the like, but this method, is not efficient because a large amount of solvent or detergent is required. It is also not economical to throw away the used solvent as it is without reusing the same.
Moreover, many kinds of solutions of organic polymers such as gravure printing inks, oiliness coating materials and coating agents utilize a number of highly inflammable and volatile organic solvents as solvents obtained by combining these organic solvents with specific ratios in accordance their use. These polymer solutions form stiff films on the surfaces of members or units of the printing machine when the solutions volatize and dry, and the washing-out of the dried materials is usually performed by using detergents consisting of organic solvents of substantially similar types to the organic solutions to be used. Thus, the washing operation requires many kinds of organic solvents as detergents, and in addition, the use of volatile and inflammable washing solvents requires much care to exhaust vapours of these washing solvents for safeness and labour for the workers.